There are currently an estimated 40,000 incidences of cardiac arrest every year in Canada, most of which take place outside of hospital settings. The odds of an out-of-hospital cardiac arrest currently stand at approximately 5%. In the U.S., there are about 164,600 such instances each year, or about 0.55 per 1000 population. It may be desirable to decrease the number of deaths resulting from these out-of-hospital incidences of cardiac arrest. Certain places, such as sports arenas, and certain individuals, such as the elderly, are at particular risk and in these places and for these people, a convenient solution may be the difference between survival and death.
Cardiopulmonary resuscitation (CPR) is an effective technique that enables medical and non-medical professionals to increase the chance of survival for patients experiencing cardiac failure. CPR forces blood through the circulatory system until professional medical help arrives, thereby maintaining oxygen distribution throughout the patient's body. However, the quality of CPR is often poor. Retention of proper CPR technique and protocol may be inadequate in most individuals and the anxiety of an emergency situation may confuse and hinder an individual in delivering proper treatment. Therefore, a device to facilitate the proper delivery of CPR in an emergency may be useful. A number of devices exist to deliver objective feedback to a CPR administrator while delivering CPR, but these devices all possess a similar inadequacy. A recent study (Resuscitation. 2009 January; 80(1):79-82. Epub 2008 Oct. 25: ‘Compression feedback devices over estimate chest compression depth when performed on a bed’) unearthed a flaw affecting current CPR assist devices. The study indicates that CPR assist devices tend to overestimate chest compression depth when the patient receiving the CPR is on a non-rigid or deformable (e.g., compressible) surface, such as a mattress. The feedback device may erroneously register the movement of the mattress as part of the chest compression. A non-rigid or deformable surface below a patient during CPR may absorb a portion of the force applied by the CPR administrator to the chest of the patient. As a result, the surface beneath the patient may be compressed downward along with the patient's chest during the compression. Any compression measuring device placed on the chest of the patient will measure both the displacement of the chest as well as the displacement of the soft surface beneath the patient. Consequently, the device may underestimate chest compression depth ultimately resulting in shallow compressions during CPR. The calculation of other compression parameters, such as chest recoil or compression force, may also be negatively affected when CPR is performed on a non-rigid or deformable surface. For example, a deformation of about 0.5 cm or larger in the surface supporting the patient may result in unacceptably erroneous sensor measurements, in some situations.
One factor contributing to this problem is the choice of sensor used to measure the chest compression depth. For example, an accelerometer is typically unable to compensate for the movement of a deformable surface, such as a mattress, because its measurements are relative to the Earth rather than the surface beneath the patient. Any motion relative to the Earth will be recorded by the accelerometer. Furthermore, the sensor typically is not able to distinguish between various sources of movement.
Other CPR assist tools use mechanical force measurements as an indicator of chest compression depth. These devices are also prone to errors when the CPR is performed on a patient supported on a non-rigid surface. The force required to compress the patient's chest a certain distance is larger on a non-rigid surface due to that surface absorbing much of the applied force. However, the device is usually unable to differentiate between the force absorbed by the mattress and that absorbed by the victim's chest.
Presently, backboards and cardioboards are used to improve the transfer of force to the chest of a patient during CPR. A cardioboard is a relatively rigid or non-deformable support platform that may be slid or placed behind the back of the patient providing a solid, flat foundation between the mattress and the patient. The cardioboard may distribute the force over a larger surface area resulting in a smaller movement of the underlying mattress. A backboard operates in a similar way.
CPR on a non-rigid or deformable surface is a common situation in the clinical setting where CPR is often performed on a padded gurney or hospital bed. In other situations, potential non-rigid or deformable surfaces include outdoor soft turf, wet ground, or carpeted floor. It may be desirable to provide a device to take into account the motion and/or displacement of the surface when determining CPR parameters such as compression depth and rate when CPR is performed on a non-rigid or deformable surface. It may also be desirable to provide a device that may be used with currently available tools such as the cardioboard and the backboard.